1. Field
This invention relates to theater (stage) lighting systems which regulate the luminescence of incandescent lamps. Specifically, this invention provides for a unitized main power unit for use in a theater lighting system wherein the cabinet includes a chassis, main power apparatus drawers, control circuit boards, a power bus unit and equipment rack.
2. State of the Art
A typical theater (stage) lighting system of today is a combination of electrical and electronic components and circuitry. Many of these systems employ solid state electronic circuitry to control the conductivity and, in turn, the power passed by controllable solid state main power apparatus (e.g., silicon-controlled rectifiers (SCR's) and TRIACS) to the incandescent lamps. Normally a plurality of external signal sources supply control signals to a corresponding plurality of control circuits. The control circuits in turn control the conductivity of a corresponding plurality of main power apparatus. The main power apparatus typically supply the power (as regulated by the control circuit) to a selectably variable number of lamps through a patch panel.
Conventionally, each system is made to order (physically and electrically) for a specific application. As constructed, these systems often include a control console which contains the external signal sources and one or more equipment cabinets which contain a plurality of drawers. The drawers, which are removably installed in a chassis contain the control circuitry and the main power apparatus.
The systems as above described are quite costly and difficult to maintain. The main power apparatus generate an appreciable amount of heat which adversely affects the other components and circuitry located in each drawer. Heat induced failures are not uncommon. Notably the drawers are very costly as they contain many components and much circuitry. Thus, many users are inhibited by cost alone from procuring a readily available spare or from acquiring a replacement after failure. In many cases replacement drawers are totally unavailable because the drawers for the particular system were tailor made and have no interchangable counterpart. Similarly, intermediate distributors are prohibited from stocking replacement drawers because of their singular application and/or high cost.
Moreover, it is quite difficult to repair a failed drawer. First, the components and circuitry are fixedly secured (e.g., hard wired) in the drawer, making replacement of defective components difficult. Secondly, sophisticated trouble shooting, often with the drawer energized (hazardous), is needed to diagnose the failure and pinpoint the defect. Accordingly the costly services of a highly skilled technician are needed. Returning a defective drawer to its manufacturer for repair is a feasible alternative; but this too is costly and the time delay may frequently be intolerable by the very nature of the theater business itself.
Many of the dimming systems above described also include direct on-off (non-dim) circuits. A few non-dim circuits are normally provided in each dimming system. These circuits are included because they provide operational flexibility. The non-dim circuits normally include an on-off device in series with a main power apparatus drawer. The on-off device is normally comprised of mercury contacts and holding relays. The voltge applied to the lamps by a non-dim circuit is generally higher (e.g., about 6 volts) than the maximum voltage available from a dimmed circuit. The result is inconsistent maximum illumination between dimmed and non-dim circuits. Operator confusion and error is a frequent result. Further, the cost of providing a non-dim circuit is quite high. An expensive main power apparatus drawer of the same type and configuration as used elsewhere in the system are normally used. Extensive engineering costs arise from the design work needed to provide the non-dim circuit capability. Also additional costs are incurred in obtaining the extra components (e.g., switches and relays) needed for the non-dim circuit. Additional maintenance costs also arise.